The present invention relates to improvements of a stacker crane.
In an automatic warehouse, a stacker crane is used as a transfer device wherein a cylindrical mast is provided on a lower cart so that an elevating platform can be elevated and lowered along the mast. Since the mast is rigid and is, for example, 30 m in height, the mast is thus very heavy. Correspondingly, the stacker crane is heavy and operates at a low speed.
It is an object of the present invention to provide a light stacker crane operating at a high speed.
It is an additional object of the present invention to reduce the weight of the mast to facilitate an increase in speed of the stacker crane.
It is an additional object of the present invention to reduce an unbalanced load on the mast to further reduce the weight.
It is an additional object of the present invention to allow the stacker crane to be smoothly driven at a high speed in order to improve the transfer capability of the stacker crane.
It is an additional object of the present invention to provide a specific mechanism for transmitting thrust to the mast.
It is an additional object of the invention to absorb vibration in the mast.
A stacker crane according to the present invention is characterized by having an upper cart provided at the top of a mast, a running motor and running wheels provided in each of a lower cart and the upper cart, and control means for controlling at least one of the running motors so that the upper and lower carts overlap each other on a vertical line.
Preferably, the upper and lower carts each have a position-recognizing means such as a laser range finder, and the control means is configured so as to allow the upper and lower carts to overlap each other on a vertical line by controlling the running motor for the cart running ahead, in a manner synchronizing with the running motor for the cart running behind.
In addition, preferably, the mast of the stacker crane is formed into a truss structure comprising a plurality of columnar members.
Further, preferably, the mast is slidably connected to at least one of the upper and lower carts.
In addition, preferably, the mast is elastically connected to at least one of the carts.
Further, preferably, the mast is connected to at least one of the carts via dampers.
According to the present invention, the lower cart is provided at the bottom of the mast, while the upper cart is provided at the top of the mast. The lower and upper carts each have the running motor and the running wheels so as to run by means of these components. The running motors are controlled so that the upper and lower carts overlap each other on a vertical line. When the upper and lower carts overlap each other on a vertical line, the mast is subjected to no force acting in a horizontal direction of the stacker crane, so that the weight of the mast can be reduced. Then, the upper and lower carts are driven relative to this mast with a reduced weight, thereby increasing the speed of the stacker crane.
According to the present invention, the upper and lower carts are allowed to overlap each other on a vertical line by controlling the running motor for the cart running ahead, in a manner synchronizing with the running motor for the cart running behind. As a result, the upper and lower carts can be allowed to constantly overlap each other on a vertical line.
According to the present invention, the mast is formed into a truss structure, thereby reducing the weight of the mast and further increasing the speed of the stacker crane.
According to the present invention, since the mast is slidably connected to at least one of the upper and lower carts, control errors between the upper and lower carts are absorbed by sliding of the mast to prevent an excess force from being applied to a connection between each of the carts and the mast. The cart to which the mast is slidably connected applies a thrust to the mast depending on the amount of sliding. If, for example, the amount of sliding is zero, almost no force is applied to the mast to allow this cart to run by means of a thrust from the other cart. Consequently, the stacker crane can be run at a high speed, and the connection between the mast and the cart is prevented from being subjected to an excess force.
According to the present invention, since the mast is elastically connected to the one of the carts, an elastic force can be applied to the mast as a thrust, depending on the amount of sliding.
According to the present invention, the dampers serve to prevent the mast from vibrating and in particular to promptly end vibration of the mast when the stacker crane is stopped, thereby reducing the time required before a loading operation can be started.